1. Field of the Invention
The invention relates to a process for producing an expanded sole, more particularly to a process in which an unexpanded blank is formed in a preliminary mold and then subjected to an inspection prior to forming into an expanded sole in a high temperature mold for expansion and crosslinking.
2. Description of the Related Art
Various processes are available for producing expanded soles from polyethylene vinyl chloride (EVA). In one of the processes, a molten EVA composition is fed directly into a high temperature mold where the composition will undergo reactions for expansion and cross-linking. In another processes, EVA compositions are first formed into sheets or other forms which are then cut and placed in a high temperature mold for forming into a final product.
U.S. patent application Ser. No. 09/157,622 which was filed by the Applicant of the application discloses a two-stage molding process for the production of an expanded sole from EVA wherein a molten EVA composition is first fed into a preliminary mold to form an unexpanded blank which is then inspected for quality control, and the qualified blank is subsequently placed in another mold to undergo a reaction for expansion and cross-linking of the blank. This two-stage process is aimed at solving the problems encountered with a conventional single-stage process in which a molten material is fed directly into a high temperature mold to undergo reactions for expansion and cross-linking. Especially, the two-stage process does not require expensive high-pressure operating hydraulic molds, and minimizes non-recyclable waste by preliminarily forming a recyclable unexpanded blank for product inspection prior to forming of the blank in a high-temperature second mold to undergo a reaction for expansion and cross-linking. The unexpanded blank, upon inspection, is combined with an additional material, if underweight, or is cut out partially, if overweight, or otherwise is recycled so that no waste is produced after the final heating stage. However, the two-stage process as disclosed therein suffers from a drawback in that, as the cavities in the first and second molds are substantially the same in dimensions, the blank formed in the first mold would substantially fit the cavity of the second mold, resulting in difficult placement of the blank in the second mold and difficult venting of air from the second mold when the unexpanded blank is formed in the second mold.